The present invention relates generally to coin operated telephones and deals more specifically with apparatus for preventing fraudulent calling initiated with a "tip-to-ground" fraud condition to defeat detection of a coin collector supervisory signal at the telephone instrument.
Coin operated telephone instruments are well known and understood in the art and the problem of fraudulent calling due to the generation of coin deposit audio signals to simulate coin deposit into the telephone instrument is also well recognized. Accordingly, there are numerous devices and proposed solutions for preventing acoustically oriented fraudulent calling and include, in some instances, complex circuit arrangements in the telephone instrument and in the various telephone offices serving the telephone instrument. However, none of the known prior devices recognize or prevent fraudulent calling due to "tip-to-ground" fraud conditions which is commonly referred to the telephone industry as "pin fraud". It is estimated that revenues lost in the United States alone due to "pin fraud" may approach millions of dollars annually.
"Pin fraud" describes a type of fraudulent calling where a pin or other small metallic object is inserted into the transducer or transmitter element in the mouthpiece of the handset and which pin is used as a contact to electrically short circuit the telephone subscriber line to ground potential to prevent the coin collect supervisory electrical signal from operating the coin collect circuitry within the telephone instrument, thereby, causing coins temporarily held in a coin hopper to be returned to the telephone user rather than the coin collection box within the telephone instrument. It is also possible to commit "pin fraud" by inserting the pin into the transducer or receiving element in the earpiece of the handset to provide the contact for short circuiting the telephone line to ground potential. Although the transmitter and receiver elements are generally used as the access points for initiating a "tip-to-ground" fraud condition, the fraud condition may also be introduced through the cord connecting the handset to the telephone instrument.
Therefore, it is an object of the present invention to provide an anti-fraud device for use with a coin operated telephone instrument which prevents fraudulent calling due to "pin fraud".
It is a further object of the present invention to provide apparatus for preventing fraudulent calling due to "tip-to-ground" fraud conditions which prevent the collection of deposited coins.
It is a yet further object of the present invention to provide an anti-fraud device which is located internally in the telephone instrument housing and without the requirement of additional special circuitry in the telephone office serving the telephone instrument.